Friday B B, Horsley V, Pavlath G K
Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
J Cell Biol. 2000 May 1;149(3):657-66. doi: 10.1083/jcb.149.3.657.
Differentiation of skeletal muscle myoblasts follows an ordered sequence of events: commitment, cell cycle withdrawal, phenotypic differentiation, and finally cell fusion to form multinucleated myotubes. The molecular signaling pathways that regulate the progression are not well understood. Here we investigate the potential role of calcium and the calcium-dependent phosphatase calcineurin in myogenesis. Commitment, phenotypic differentiation, and cell fusion are identified as distinct calcium-regulated steps, based on the extracellular calcium concentration required for the expression of morphological and biochemical markers specific to each of these stages. Furthermore, differentiation is inhibited at the commitment stage by either treatment with the calcineurin inhibitor cyclosporine A (CSA) or expression of CAIN, a physiological inhibitor of calcineurin. Retroviral-mediated gene transfer of a constitutively active form of calcineurin is able to induce myogenesis only in the presence of extracellular calcium, suggesting that multiple calcium-dependent pathways are required for differentiation. The mechanism by which calcineurin initiates differentiation includes transcriptional activation of myogenin, but does not require the participation of NFAT. We conclude that commitment of skeletal muscle cells to differentiation is calcium and calcineurin-dependent, but NFAT-independent.
定向分化、细胞周期退出、表型分化，最终细胞融合形成多核肌管。调节这一进程的分子信号通路尚未完全清楚。在此，我们研究钙和钙依赖性磷酸酶钙调神经磷酸酶在肌生成中的潜在作用。根据表达每个阶段特有的形态学和生化标志物所需的细胞外钙浓度，将定向分化、表型分化和细胞融合确定为不同的钙调节步骤。此外，在定向分化阶段，用钙调神经磷酸酶抑制剂环孢素A（CSA）处理或表达钙调神经磷酸酶的生理抑制剂CAIN均可抑制分化。逆转录病毒介导的组成型活性钙调神经磷酸酶基因转移仅在细胞外钙存在的情况下才能诱导肌生成，这表明分化需要多种钙依赖性途径。钙调神经磷酸酶启动分化的机制包括肌细胞生成素的转录激活，但不需要NFAT的参与。我们得出结论，骨骼肌细胞向分化的定向分化是钙和钙调神经磷酸酶依赖性的，但与NFAT无关。
